Insulators currently used for supporting a conductor within an enclosure, such as, for example, isolated phase bus duct, are supported by an aluminum plate that is in turn bolted to wings welded to the inside of the enclosure. The conductor is mounted to the insulator by a bolt that passes through the conductor and the central axis of the conductor. In the event of a short-circuit condition, a force is applied to the conductor of each phase of the bus ducts that tries to move the conductor to a zero force line. Because the insulators are typically made from ceramic compositions, they are less able to withstand the shearing action associated with the movement to the zero force line than the compressive load to which the insulators are normally subjected. These forces are greater than those that can be compensated for by any inherent flexibility in the aluminum plate to which the insulator is mounted. As a result, mechanical force formulas have been developed to determine the maximum span or distance between insulators along each bus duct run. For high short-circuit requirements, the span between insulators is relatively small so as to maintain the conductor in place and prevent the conductor from moving to the zero force position and potentially damaging the insulators. This results in a rather expensive bus duct configuration using many insulators.
U.S. Pat. No. 2,396,131 issued to Scott, Jr. discloses a bus bar support where insulators are provided with a universal ball and socket type joint to compensate for movement of the conductor relative to the enclosure due to thermal expansion and contraction of the conductor. However, this patent discloses four such insulators for each connection point with the enclosure. Hence many insulators are required giving rise to an expensive bus duct configuration. Further, the insulator is reinforced at the universal joint with a steel bearing sleeve threaded into the insulator that nests in the insulator a spring washer to provide the socket portion of the universal joint. This configuration is costly to manufacture.
Accordingly, there is a need for an insulator arrangement that addresses forces associated with short-circuit conditions and the stress placed on the insulator during such short-circuit conditions.